Faced fibrous insulation is used in a variety of thermal and acoustical applications. Conventional insulation assemblies used in HVAC units typically include a facing layer adhered to a fibrous insulation layer. The facing layer is useful in preventing or at least limiting any air erosion damage which may be caused by the flow of air directly across the insulation layer.
One example of a conventional faced fibrous insulation product is disclosed in U.S. Pat. No. 6,444,289. U.S. Pat. No. 6,444,289 discloses the use of non-porous aluminum foil, foil reinforced paper, foil scrim paper, or polymeric material which is adhered to the fibrous insulation by an adhesive. Perforations are formed in the facing layer after the facing layer and the insulation layer are joined and the adhesive bond is set or cured.
U.S. Pat. Nos. 5,783,268 and 6,270,865 disclose that faced fibrous insulation used in duct board provides an air flow surface with increased air flow and less turbulence. The faced fibrous insulation also provides a smooth surface that reduces the accumulation of dirt and dust. In addition, U.S. Pat. Nos. 5,783,268 and 6,270,865 disclose the use of a central layer of compressed fiberglass one or one and one half inches thick with a polyester/glass mat facing having a density of about 0.01 pounds per square foot, a minimum tensile strength of 7 pounds/inch in the machine direction, and 5 pounds/inch in the cross-machine direction. The fibrous insulation is formed by the industry standard rotary fiber process, as developed by Owens Corning, in which molten glass is spun into fibers by a perforated spinner and blown by high temperature gas to elongate the individual fibers. The fibers are then sprayed with a phenol-formaldehyde binder to form an uncured pack of glass fibers. The mat facing is then applied to the pack of glass fibers so that the mat facing is adhered to the fiberglass solely by the uncured binder in the pack when the pack and facing are cured.
The '268 and '865 patents also disclose the formation of shiplap edges at the outer edges of the duct board to assist in the fabrication of a fiberglass duct. However, this method tends to result in poor adhesion of the mat facing to the fibrous insulation due to the inherent difficulty in controlling the amount of binder at the surface. The method also tends to increase manufacturing costs because the process of curing the fibrous insulation must be optimized to provide a suitable bond between the mat facing and the glass fibers rather than optimizing for improved efficiency in curing the binder in the pack of fibers.
In addition to the method disclosed in the '268 and '865 patents, it is known in the art to manufacture faced insulation by spraying a binder directly onto the facing prior to application of the facing to an uncured pack of fibers and subsequently curing the binder in the pack and on the facing. For example, U.S. Pat. No. 5,041,178 discloses spraying a binder onto the interface where the facing meets the upper and lower surfaces of the uncured pack. This method tends to saturate the fibers on the surface of the finished board which causes a brashy surface on the fibrous insulation due to the fiber ends which are fixed in place by the high amount of binder at the surface. The high amount of binder on the mat also may cause discoloration of the mat facing causing a spotty or mottled surface on the fibrous insulation.
Faced fibrous insulation may also be formed by applying a polymer directly to the surface of a cured fiberglass pack. U.S. Pat. No. 5,900,298 discloses the use of a row of spiral spray extrusion heads for directly extruding ethyl vinyl acetate (EVA) fibers onto the cured pack of fibers in an amount of 1.2 to 3.5 g/ft2. U.S. Pat. No. 5,487,412 discloses a duct board including an applied layer of an acrylic foam coating having a dry solids content of 10-20 g/ft2 of the surface of the board. The coating also includes an inorganic biocide such as silver nitrate.